Table
8-2: Examples of regional impacts of climate change on water resources,
land degradation, and desertification.

Region

Projections

Reference Section in WGII TAR

Africa

Changes in rainfall and intensified land use would exacerbate the
desertification processes.
Desertification would be exacerbated by reduction in the average annual
rainfall, runoff, and soil moisture in countries of west African Sahel,
and northern and southern Africa (medium confidence).
Increases in droughts and other extreme events would add to stresses
on water resources, food security, and human health, and would constrain
development in the region (high confidence).

Water shortage -- already a limiting factor for ecosystems, food
and fiber production, human settlements, and human health -- may
be exacerbated by climate change. Runoff and water availability may
decrease in arid and semi-arid Asia but increase in northern Asia
(medium confidence). Reduced soil moisture in summer would
exacerbate land degradation and desertification in arid and semi-arid
regions.

Interannual variability due to ENSO leads to major floods and droughts
in Australia and New Zealand. Such variations are expected to continue
under enhanced greenhouse gas conditions, but possibly with greater
hydrological extremes.
Water is likely to be a key issue (high confidence) due to
projected drying trends over much of the region and change to a more
El Niño-like event state. Water quality would be affected,
and more intense rainfall events would increase fast runoff, soil
erosion, and sediment loading. Eutrophication is a major water quality
problem in Australia.

Summer runoff, water availability, and soil moisture are likely
to decrease in southern Europe, and would widen the gap between the
north and south (high confidence). Flood hazards will increase
across much of Europe (medium to high confidence); risk would
be substantial for coastal areas where flooding will increase erosion
and result in loss of wetlands. Half of alpine glaciers and large
permafrost areas could disappear by the end of the 21st century (medium
confidence).

Some studies based on model experiments suggest that under climate
change the hydrological cycle would be more intense, with changes
in the distribution of extreme rainfall, wet spells, and dry spells.
Frequent severe drought in Mexico during the last decade coincides
with some of these model findings. El Niño is related to dry
conditions in northeastern Brazil, northern Amazons, and the Peruvian-Bolivian
altiplano. Southern Brazil and northwestern Peru exhibit anomalous
wet conditions during these periods.
Loss and retreat of glaciers would adversely impact runoff and water
supply in areas where snowmelt is an important water resource (high
confidence).

Snowmelt-dominated watersheds in western North America will experience
earlier spring peak flows (high confidence) and reduction
in summer flow (medium confidence); adaptive responses may
offset some, but not all, of the impacts on water resources and aquatic
ecosystems (medium confidence).

All three classes of freshwater problems -- having
too little, too much, and too dirty water -- may be exacerbated by climate
change. Freshwater is essential for human health, food production,
and sanitation, as well as for manufacturing and other industrial uses and
sustaining ecosystems. There are several indicators of water resources stress.
When withdrawals are greater than 20% of the total renewable resources,
water stress often is a limiting factor on development. Withdrawals of 40%
or more represent high stress. Similarly, water stress may be a problem
if a country or region has less than 1,700 m 3 yr-1 of water
per capita. In the year 1990, approximately one-third of the world's
population lived in countries using more than 20% of their water resources,
and by the year 2025 about 60% of a larger total would be living in such
a stressed country, only because of population growth. Higher temperatures
could increase such stress conditions. However, adaptation through appropriate
water management practices can reduce the adverse impacts. While climate
change is just one of the stresses on water resources in this increasingly
populated world, it is clear that it is an important one (see Table 8-2).
The TAR projections using the SRES scenarios of future climate indicate
a tendency for increased flood and drought risks for many areas under most
scenarios. Decreases of water availability in parts of a warmer world are
projected in areas like southern Africa and countries around the Mediterranean.
Because of sea-level rise, many coastal systems will experience saltwater
intrusion into fresh groundwater and encroachment of tidal water into estuaries
and river systems, with consequential effects on freshwater availability.

Water managers in some countries are beginning
to consider climate change explicitly, although methodologies for doing
so are not yet well defined. By its nature, water management is based
around minimization of risks and adaptation to changing circumstances, now
also changing climate. There has been a gradual shift from "supply-side"
approaches (i.e., providing water to satisfy demands by increased capacity
reservoirs or structural flood defenses) towards "demand-side"
approaches (i.e., trimming demands adequately to match water availability,
using water more efficiently, and non-structural means of preparedness to
floods and droughts).